A Level Biology Revision Notes

Comprehensive A Level Biology revision notes providing information and assistance for all UK examination boards (AQA, OCR, Edexcel) as well as international curriculum (CIE).

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Skeletal Muscles

Introduction Skeletal muscles are the most abundant tissue forum in the human body. More than 40% or our body is made up of skeletal muscles. These are the voluntary muscles that are under the control of the somatic nervous system. Most of the skeletal muscles are attached to bones via specialized connective tissues. In this …

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Prokaryotic vs Eukaryotic

Introduction Living organisms are divided into two groups based on the primary differences in the cellular structures; prokaryotes and eukaryotes. It has been believed that prokaryotes were the first organisms to appear on earth. The rest of the higher organisms evolved from these simple prokaryotic organisms.  They differ in terms of cellular structures, body forms, …

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Messenger RNA (mRNA)

Introduction Ribonucleic acid or RNAs are the working copies of DNA. The information present in DNA is expressed in the form of these working copies. Three major types of RNA are found in all the living cells; messenger RNA, ribosomal RNA, and transfer RNA.  The messenger RNA (mRNA) carries the message of DNA from the …

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Histone Acetylation

Introduction The genetic material in living organisms is present in the form of DNA. This DNA does not lie within the cell in the form of threads. Rather, DNA in eukaryotes is organized into higher structures to keep it compact so that it can fit into the nucleus.  The DNA in eukaryotes is wound around …

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Conservation of Environment

Introduction Conservation of the environment is a set of methods and practices which are observed to preserve the environment, its inhabitants, and the resources it provides. There is a need for conservation of the environment as there is continuous inflation of population, pollution, and consumption of resources. We must learn to protect and conserve nature …

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Epigenetics

Introduction The tern ‘Epigenetics’ is used for the changes in DNA that can alter phenotype or trait without altering the nucleotide sequence present in the DNA. These are the heritable changes that can affect gene expression. Any change in gene expression will lead to a change in the phenotype of that gene or the trait …

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Gene Expression

Introduction The genetic information is present in all the organisms in the form of DNA. This DNA is present in the nuclei of eukaryotic cells and contains the information for all the traits expressed by the cell. The genetic material controls al the traits of a cell by guiding and controlling the synthesis of proteins.  …

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Gene Mutations

Introduction A gene is a part of DNA that codes for the synthesis of one protein. The entire DNA is made up of thousands of genes that directly control all the functions of a cell via protein synthesis. The sequence of nucleotides in a gene determines the sequence of amino acids in a polypeptide. Therefore, …

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Meselson–Stahl Experiment

Discovery and History After the brilliant work of describing the DNA structure, Watson and Crick also proposed a hypothesis that the DNA replication process is semi-conservative. This hypothesis was strengthened by the experiment of Meselson and Stahl in which they elucidated the nature of replication of DNA. The cell was first discovered to be dividing …

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